Bidirectional association between tobacco use and depression risk in the SUN cohort study.

We assessed the association of tobacco use or smoking cessation with depression risk and determined if the presence of a depressive disorder was associated with smoking onset. We conducted a prospective cohort study (SUN Project) based on 16,519 Spanish university graduates without depression at baseline. Tobacco use was determined at baseline and after four years of follow-up. Incident cases of depression were ascertained according to a previously validated report of a clinical diagnosis of depression during follow-up. Multivariable Cox regression models were used to estimate hazard ratios (HR) of depression according to previous smoking status. We used logistic regression models as a secondary analysis to estimate Odds Ratios (OR) of smoking onset during the first four years of follow-up according to lifetime depression prevalence at baseline. The multivariable HR (95% CI) for current smokers was 1.24 (1.05-1.46) as compared to participants who had never smoked. Participants with the highest exposure to tobacco (≥ 20 packs-years) had a significant 38% relative increment in depression risk. Smoking cessation during the first four years of follow-up was inversely associated with depression (HR = 0.63; 95% CI = 0.40-0.99). Finally, a significant increment in the risk of smoking onset for participants with lifetime depression prevalence was observed (multivariable OR = 1.44; 95% CI = 1.13-1.83). A bidirectional association between tobacco use and depression in the SUN cohort was found. Therefore, tobacco control and health promotion campaigns for smoking cessation could be considered as effective strategies of public health for the prevention and management of depressive disorders.